A fundamental paradigm of IBD pathogenesis is that inflammation results from an inappropriate response to the pathogen-associated molecular patterns (PAMPs) expressed by the gut microbiota. Recent evidence from other immune-mediated disorders indicates that chronic inflammation occurs when PAMP signals are combined with signals derived from tissue damage, the so-called damage-associated molecular patterns (DAMPs). These are released by injured/dead cells and induce a sterile inflammatory response. DAMPs are numerous, including the high mobility group protein 1 (HMGB1), nucleic acids, uric acid, degradation products of the extracellular matrix, calcium-binding S100 proteins, and many others. DAMPs utilize receptors shared with PAMPs, such as Toll-like receptors (TLRs), but also distinct receptors, co-receptors and accessory molecules to mediate their actions. Some DAMPs have already been identified in IBD, such as HMGB1 and calcium-binding S100 proteins and, therefore, understanding how their signals converge with those coming from PAMPs becomes obviously relevant and will be explored in this proposal. The cytokine IL-1? has been recently identified as a major DAMP released by necrotic cells and is a strong inducer of sterile inflammation. Because the IL-1 cytokine family is involved in IBD, we performed preliminary studies and found that necrotic intestinal epithelial cells release IL-1?, which induces proinflammatory events in the gut. We also found that IL-1? is present in vivo in the epithelium and can trigger experimental colitis. Thus, we propose the novel central hypothesis that epithelial cell-derived IL-1? is a major intestinal DAMP and represents a novel component of IBD pathogenesis. This hypothesis will be tested by 3 specific aims: Aim 1. Characterize the response of human immune and non-immune cells to necrotic cell-derived IL-1? alone and in combination with other DAMPs and PAMPs. Aim 2. Determine the mechanisms by which necrotic cell-derived IL-1? regulates the inflammatory response. Aim 3. Explore the role of necrotic cell-derived IL-1? in induction and modulation of intestinal inflammation in vivo. The innovative concept that epithelial-derived IL-1? can mediate inflammation alone or in association with PAMPs would create a paradigm shift in our current understanding of IBD pathogenesis. Additionally, interfering with the DAMP function of IL-1? may generate new insights into how to modulate intestinal immunity and inflammation.